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FLTK Help Session

FLTK Help Session. By Richard Yu Gu CS 638 -Graphics Fall, 1999. Component of FLTK to Discuss. Widget Basics Sub-classing Widgets Basic Drawing Event Handling Questions. Building blocks Several widgets can behave independently or interrelated

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FLTK Help Session

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  1. FLTK Help Session By Richard Yu Gu CS 638 -Graphics Fall, 1999

  2. Component of FLTK to Discuss • Widget Basics • Sub-classing Widgets • Basic Drawing • Event Handling • Questions

  3. Building blocks Several widgets can behave independently or interrelated Many different “build-in” types come with FLTK Window Button Box Input Field File Chooser Menu Slider Group Widgets in FLTK

  4. Window by Example • Creating a new Window with its size as parameters • Subsequent Widget creation are to this window until end() occur. • show() member method displays the window • damage(1) member method triggers refreshing of the window

  5. Box by Example • Add Box to a window with its position in the window and its size. • redraw() method refreshes and update the display of the box, which is triggered by damage(1). • label() method allow drawing of text or image to the box.

  6. Buttons and Callback Functions • Button respond to click on them by calling the pre-registered function- “callback” function • Register a callback function by using the member function callback(<func name>, <(list of) parameters to the CB func>). • Define callback function as void funcname(Fl_Widget *but, <parameters>)

  7. Sidetrack on Callback Functions • Callback functions can be used and is meaningful for most of the widgets in FLTK library • When the default event of the widget occurred, the registered callback function if invoked automatically.

  8. #include <FL/fl_draw.h> color(x) to change color <FL/Enumerations.H> to see pre-defined colors Override draw() func of the widget to make the drawing persistent fl_rectf fl_rect fl_line fl_loop fl_polygon fl_arc fl_pie fl_draw(char *, int x, inty) Drawing Using FLTK

  9. Image Stored as char array, image, of length width*height*3. (Ordered in RGB) fl_draw_image(image, X, Y, imgW, imgH) With in a widget such as box do the following (new Fl_Image((unsigned char *)(image), imgW, imgH))->label(this); Drawing Images To make the drawing persistent programmer should subclass the widget that which to be drawn to and override the private: void draw() function.

  10. Event Handling • User Interaction • Mouse and Keyboard • Actions • Subclass the widget that need to deal with some specific events • Override the public: int handle(int e) method in the new class. • If, in the handle() function an event is dealt with, function should return 1, otherwise return 0.

  11. Event Handling Cont. • To find out where the mouse is use • Fl::event_x(); • Fl::event_y(); • To find out which button is pressed • Fl::event_button(); • To find which key is pressed • Fl::event_key(); • Parameter e tells the type of event, common types are • FL_PUSH • FL_DRAG • FL_RELEASE • FL_RELEASE • FL_MOVE • FL_KEYBOARD

  12. Questions? • More example of widgets? • More details at S:\fltk\documentation • Questions?

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